How can I show product reviews on the recommendations widget

To show the product reviews, you have to access the 'App preferences section' (How can I access the app preferences page?).

After you have accessed it, you need to select the Visual styles:

Click on the Rating section (or the score stars on the image):

Here, you will be able to configure the app with the review app you are using to display the product ratings, as well as modify multiple visual aspects of it.